JPS6312767B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel polyethylene stretch molded article. British Patent Application No. 10746/73 describes molded articles,
In particular, Young's modulus (dead load creep) is 3.
×10 There is a description of high-density polyethylene filaments, films, and fibers of ¹⁰ N/m ² or more, and the weight average molecular weight (w) is
200000 or less, number average molecular weight (n) is 20000 or less, and when n is ¹⁰⁴ or more, w/n is 8 or less,
When n is ¹⁰⁴ or less, a polymer with w/n of 20 or less is cooled from a temperature near its melting point at a rate of 1 to 15°C per minute, and then the cooled polymer is stretched to form high modulus polyethylene. Goods are being obtained. We define crystalline polymers as having more than one (i.e., two or more) molecular chains of a given molecular chain.
The Young's modulus is reduced to 3 by subjecting the polymer to heat treatment under conditions that substantially reduce the possibility of its incorporation into crystalline lamellae, and by stretching the polymer at a speed and temperature such that the molecules become almost perfectly linear. ×10 ¹⁰ N/
We have discovered the fact that a polymer material with a high modulus larger than m ² can be obtained. That is, the present invention (1)200000<w〓300000
(w: weight average molecular weight) high density polyethylene,
(2) high-density polyethylene with weight average molecular weight (w) < 200,000 and number average molecular weight (n) = 20,000;
and (3) when weight average molecular weight (w) < 200000, number average molecular weight (n) < 20000 and n = 10 ⁴ ,
When Mw/n>8 and n<10 ⁴ , w/
High modulus oriented high-density polyethylene having a Young's modulus greater than 3×10 ¹⁰ N/m ² when measured at room temperature under a strain of 0.1% for 10 seconds, selected from the group consisting of high-density polyethylene with Mn > 20. This invention relates to a stretched molded product. As used herein, a crystalline polymer refers to a polymer that can form a crystalline or semi-crystalline structure when its melt is cooled. High density polyethylene is defined herein as a substantially linear ethylene homopolymer or copolymer containing at least 95 weight percent ethylene and having a density of 0.91 to 1.0 g/cm ³ . The density is based on British Standard Specification No. 3412 (1966).
Samples prepared according to Appendix A and annealed according to Appendix B (1) of the same, for example, samples obtained by polymerizing ethylene in the presence of transition metals, are used in Pretension Standard Specification No. 2782
(1970) using method 509B. The crystalline polymer should have a suitably high weight average molecular weight so that the shaped article after stretching retains favorable physical properties in terms of strength and elongation at break. However, a high concentration of long chain moieties increases the chance that a given molecular chain will be introduced into more than one crystal lamella before stretching. Hereinafter, in this specification, such a molecular chain will be referred to as an interlamellar molecular chain. Although the present invention is not limited by any particular theory, it is believed that excess interlamellar molecular chains reduce the degree of molecular orientation and linearization obtained by stretching due to increased permanent morphological entanglement; It is thought that this prevents optimal physical properties from being obtained as a result. The preferred weight average molecular weight (w) of the polymer is
50,000 to 250,000, more preferably from 50,000
150000, and the number average molecular weight (n) is from 5000
25,000, more preferably 5,000 to 15,000. Normally, in order to make the deformation at the molecular level more uniform during the elongation process, w with respect to n is
It is advantageous to avoid increasing the ratio of
The preferred ratio of w to n is 30 or less. In particular, a relatively narrow molecular weight distribution, e.g.
100 When ⁴ or more, w/n is 10 or less (preferably 8 or less, most preferably 6 or less), and n is
Good results can be obtained by using a polymer with w/n of 25 or less (most preferably 15 or less) when the ratio is 10 ⁴ or less. Molecular weights quoted herein are determined by gel permeation chromatography. Heat treatment can, for example, cause a substantial portion of molecules with intermediate molecular weights to crystallize into discontinuous, highly ordered folded chain lamellae, while small amounts of very large and very small molecular weight molecules are separated. However, in rare cases where crystalline regions are interconnected, molecular weight fractionation has the effect of reducing the possibility of introducing excess molecular chains into one or more lamellae. This effect can be obtained, for example, by the following three methods. (1) A method of cooling a polymer at a predetermined rate from a temperature at or above its melting point to an ambient temperature at which a desired crystal structure is obtained. In this case, the cooling rate depends on the molecular weight characteristics of the polymer. It is generally necessary to cool the polymer at a rate of less than 40°C per minute, preferably less than 20°C per minute. The most preferred cooling rate is 10°C per minute or less. (2) A method in which a polymer is cooled from its melting point or higher to a temperature below its crystallization temperature at a predetermined rate, and then rapidly cooled to ambient temperature. The cooling rate is preferably 1-15°C per minute, most preferably 2°C per minute.
~10℃. Preferably 5 to 20 degrees higher than the crystallization temperature
The polymer is quenched when the temperature below 0°C is reached. Quenching should preferably be at a rate of no more than 100,000°C per minute. (3) A method of rapidly cooling a polymer from a temperature at or above its melting point to near its crystallization temperature and holding the polymer at that temperature for a sufficient period of time to cause crystallization. Preferably the polymer is held at a temperature within 15°C of the crystallization temperature for 0.5 to 10 minutes.
The polymer is then preferably rapidly cooled to ambient temperature. Optical micrographs of samples prepared by methods (1), (2), and (3), respectively, show that polymers with predetermined molecular weight characteristics contain uniformly oriented regions of various sizes throughout the polymer. This shows that a structure is formed. In high density polyethylene these areas can reach up to 15μ. The conditions used in methods (1), (2) and (3) are selected based on the molecular weight characteristics of the polymer. However, in general, if the polymer has a particularly narrow molecular weight distribution, extremely slow cooling (at less than 1° C. per minute) will not produce a crystalline structure suitable for elongation. 40°C per minute in methods (1) and (2)
Making very fast cooling and methods of more than (3)
It has also been found that holding at the crystallization temperature for longer than necessary is also detrimental. Figures 1a, 1b and 1c show the methods (1) and (2) of the present invention in the case of high-density polyethylene, respectively.
and (3). As an alternative method of forming a crystalline structure that substantially reduces the possibility that a given molecular chain will be incorporated into one or more crystalline lamellae, the polymer can be heated from a temperature at or above its melting point to a temperature well below its crystallization temperature. There is a method of rapidly cooling to a temperature to obtain a relatively low degree of crystallinity. This method, namely method (4), significantly reduces the size of the spherulites and produces a crystal-containing structure surrounded by large amorphous regions, thereby reducing the number of interlamellar molecular chains. It is.
Preferably the cooling rate is greater than or equal to 1000°C per minute, most preferably greater than or equal to 5000°C per minute throughout the crystallization temperature range, and the polymer is cooled to ambient temperature or below. Depending on the molecular weight characteristics of the polymer, it may be advantageous to reheat the cooled polymer to increase the size of the crystalline regions prior to attenuation. The optical micrograph of the sample produced by method (4) clearly shows that it has a spherulite structure connected in a string like the conventional method, but it can be distinguished from Tsuritsu in that the spherulites are small. be able to. Figure 1d shows the crystal structure produced by method (4) of the invention in the case of high density polyethylene. Structures formed with different heat treatment methods do not necessarily deform in the same way under a given condition. There will be an optimal elongation method for each structure. If there is an apparent molecular orientation in the unstretched material, elongation may be undesirably limited. Polymer crystallization has been extensively studied;
Explanations can also be found in books such as Crystallization of Polymers (Chapter 8: Crystallization Kinetics and Mechanisms) by Elle Mandelkahn, published by McGraw-Hill in 1964. By observing changes in properties such as density and specific volume, it is understood that crystallization occurs in stages. There is a time lag until crystallization is observed, but as soon as it is observed, it proceeds naturally and almost autocatalytically accelerated. Eventually, the crystallization reaches a state of pseudo-equilibrium, after which crystallization proceeds very gradually over a long period of time in small but appreciable amounts. This crystallization process is continuous, and the rate of crystallization versus time is plotted in an S-shape, with no abrupt changes or discernible discontinuities. The rapid crystallization is called primary crystallization, and the slow crystallization stage is called secondary crystallization. It is believed that secondary crystallization is disadvantageous in obtaining high modulus, and while for some polymers some secondary crystallization can still provide favorable properties upon elongation; It has been found that the highest modulus is obtained when the process is not dominated by secondary crystallization. At least methods (1) and (2)
For (3) and (3), it is usually found to be advantageous to allow the crystallization to proceed until the rapid initial crystallization is substantially complete. There used to be. The progress of crystallization can be tracked by measuring the density of the polymer. In methods (1), (2) and (3), the maximum elongation achievable (maximum modulus obtained) for a given heat treatment and given polymer is determined by increasing the density until the polymer density reaches an optimum. increases with However, as the polymer density increases above the optimum density, the maximum elongation obtained will decrease. By attenuating samples of different densities under the same conditions, it is possible to determine the optimal polymer density for a given attenuation condition. After heat treatment, the polymer is stretched at a temperature and at a rate such that the deformation is at least 15, preferably at least 20. It is believed that the high degree of elongation necessary to obtain high modulus is achieved by uniform stretching and consequent orientation of the polymer, which corresponds at the molecular level to the degree of unfolding of the molecules in the crystalline lamellae. A particularly preferred attenuation method is one in which the tensile force is less than or equal to the tensile strength of the polymer, but sufficient to cause linearization of the molecules by inducing a deformation in the plastic that exceeds the elongation that would occur by flow stretching. The polymer is drawn at high draw ratios at high speeds and temperatures. Preferably the draw ratio is at least 20. Optimal stretching conditions depend to some extent on the nature of the polymer and its thermal history. In general, it is preferable to stretch the polymer relatively slowly, for example, between relatively movable clasps at a rate of 1 cm per minute or more, usually about 10 to 20 cm per minute, at a temperature of at least 40°C below the melting point of the polymer. Stretch or 30-150cm/min at a temperature of 5-20℃ below the melting point on a stretching frame
Stretch at a speed of The physical properties of the polymeric material may be further improved by stepwise stretching, with pauses in the polymer between each step, and intermittent stretching. Preferably, polymers with relatively small cross-sections are subjected to a drawing process, and the invention is particularly suitable for the production of fibers and films. In particular, continuous filaments are produced by melt spinning or by drawing on drawing frames. For convenience, the fiber diameter or film thickness before stretching is preferably 1 mm or less. As used herein, the deformation ratio or stretching ratio is defined as the ratio of the length after treatment to the length before treatment or the ratio of the cross-sectional area after stretching to the cross-sectional area before stretching. In the method of the present invention, for example, the Young's modulus defined below is 3.
×10 ¹⁰ N/m ² or more, in some cases at least 6×
10 ¹⁰ N/m ² of polyethylene polymer can be produced. Since the Young's modulus of a polymeric substance depends to a large extent on the measurement method, in this specification, the Young's modulus is determined to be 0.1 by a dead-loading creep test.
It is defined as the measured modulus at 21°C when % strain (strdin) is applied for 10 seconds. This test method is described in Gupta and Ward: Journal of Macromolecular Science and Physics, B1, 373 (1967). It can be seen that the method of the invention results in polymer molecules that are substantially perfectly linearly arranged upon plastic deformation. This molecular orientation is often uniaxial, but by applying appropriate stretching, a biaxially oriented polymer can also be obtained. Substantially perfect orientation can be determined by physical measurements such as X-ray diffraction analysis and nuclear magnetic resonance analysis. According to the method of the invention, a polyethylene material having a Young's modulus of 5×10 ¹⁰ N/m ² or more is obtained. The theoretical Young's modulus of polyethylene is 24×10 ¹⁰ N/m ²
It can be seen that the polymers of the present invention are very close to this value. The polymeric material according to the invention is manufactured in a monolithic structure. The present invention will be explained below with reference to Examples. Example 1 High-density polyethylene (described later) was heated to 190°C with a diameter of 0.1
Melt-spun through a cm die, diameter 0.06~0.07cm
An isotropic filament is obtained. The filament is wound onto a 5.5 cm diameter cylinder rotating at 2.3 rpm. The cooling rate of the polymer is set at 5°C per minute and the structure formed when the polymer temperature reaches 115°C is maintained by rapid cooling. length 3
A ~4cm sample was tested using an Instron tensile tester.
Stretch at 72°C for 30-45 seconds at a crosshead speed of 20 cm/min. The stretching ratio is determined based on the change in the cross section of the filament. Two types of polymers selected from commercially available BP high-density polyethylene are used as samples. One is 075-60 grade, melt flow index 8.0, n: 14450, w: 69100 when measured at a temperature of 190°C and a load of 2.14 kg. Others are Rigidex 9, melt flow index 0.9, n: 6060, w: 126600
It is. Measure Young's modulus for 10 seconds at room temperature (21°C). The 075-60 grade has a narrow molecular weight distribution, that is, w/n=4.8, and a stretched product with a stretching ratio of 20 and a Young's modulus of 4.0×10 ¹⁰ N/m ² can be obtained. On the other hand, Rigidex 9 has a wide molecular weight distribution, that is, a high w value of Mw/n=20.9, and as a result, a stretched product having a low Young's modulus can be obtained. Continuous filaments of the materials described above can be stretched on a stretching frame to give similar results. Example 2 By compression molding high-density polyethylene pellets between two copper plates at 160°C,
Obtain a 0.07cm thick sheet. Remove this sheet from the press and slowly press it at a rate of 7 to 9 degrees Celsius per minute.
Cool to 100°C (measured on the surface of the copper plate) and then quench in cold water. A rectangular sample with a length of 2 cm and a width of 0.5 cm was tested using an Instron tensile tester.
Stretch for 70-90 seconds at a crosshead speed of 10 cm/min. The stretching ratio is 0.2 on the surface of the sample before stretching.
Or make marks at 0.1 cm intervals and measure accordingly. Two grades of commercially available BP high-density polyethylene were used as samples. Rigidex 50 has a melt flow index of 5.5, n: 6180, w: 101450, and 140
−60 grade has a melt flow index of 12,
n: 13350, w: 67800. Rigidex 50
The maximum draw ratio for the 140-60 grade is determined to be 30 and 37-38 for the 140-60 grade. The Young's modulus of representative samples was measured at room temperature for 10 seconds, and the results are shown in the table below.

TABLE The following Examples 3 to 5 demonstrate that the maximum draw ratio obtainable occurs at the optimum density, and that the optimum density is a function of the heat treatment conditions. Example 3 High-density polyethylene (Rigidex 25, a product of BP Limited, w: 98800, n:
A film is made by compression molding 12950 at 160℃ between two 0.5mm thick copper plates. The plate is removed from the press, wrapped thickly in raw cotton, and the polymer is cooled at a rate of 5° C. per minute as measured by a thermocouple. When the temperature reaches 120 °C, place the plate in a glycerin bath maintained at 120 °C and incubate from 0 (do not enter the bath).
Hold for 10 minutes. The density of the film is measured using a density column. A dumbbell-shaped sample of the film is stretched using an Instron tensile tester at 75° C. for 60 seconds at a crosshead speed of 10 cm/min. Marks are placed on the sample before stretching at intervals of 0.2 or 0.1 cm, and the stretching ratio is determined based on the increase in length of the sample after stretching. Table 2 shows the influence of holding time at 120°C on density and maximum stretching ratio. Example 4 Example 3 except that the plate was removed from the press and immediately immersed in a glycerin bath and the polymer was cooled from 160°C to 120°C at a rate of 40°C per minute.
Process in the same way as . Table 2 shows the effect of density on drawing ratio. Example 5 A polymer is sandwiched between aluminum foils, and the whole is sandwiched between copper plates. Processing is carried out in the same manner as in Example 3, except that only the copper plate is removed immediately before placing the polymer and aluminum foil in the glycerin bath. The cooling rate is 400℃ per minute. Table 2 shows the effect of holding time at 120°C on density and maximum drawing ratio.

【table】

[Table] High-density polyethylene (Rigidex 140-60,
BP Limited products, w: 67800,
Mn: 13350) is extruded at 180° C. through an extrusion port with a 0.9 mm orifice and the resulting filament is passed through a glycerin bath maintained at 120° C. before winding. The position of the bath below the extrusion port and the retention time of the filament in the bath are varied. The temperature of the filament entering the bath is approximately 135°C. The filament is drawn under conditions similar to those described in Example 3. Table 3 shows the conditions for spinning and drawing and the properties of the drawn filament. In addition, the modulus is owned by Gupta and Ward in the Journal of Macromolecular Science and Physics.
B1, 373 (1967), measured at 21°C using the dead load creep test.

[Table] When the spun filament of Example 6 was cut and observed under a polarizing microscope, regularly oriented regions uniformly distributed throughout the filament were observed. This region represents the initial flux in spherulite growth. Example 7 The spun filament was wound at a speed of 150 cm per minute,
The process is carried out in the same manner as in Example 6 except that the bath temperature is varied from 60 to 125°C. The temperature of the filament upon entering the bath is measured with an infrared pyrometer. The properties of the spun filament are shown in Table 4. Example 8 High density polyethylene (Rigidex 140-60)
is spun into single fibers and cooled using the same apparatus as in Example 6. The employment conditions are as follows. Extrusion rate 0.3 g/min Extrusion temperature 180°C Winding speed 5 feet/min Cooling distance from spinneret 7.5 cm Cooling temperature 120°C Cooling length 50 cm The obtained drawn yarn was drawn with a drawing frame on pins maintained at 130°C. Ratio 23.8, drawing speed 1 ft/
Stretch continuously in minutes. The drawn filament obtained has a strength of 6.7 gpd tex, an elongation at break of 2.9%, and a creep modulus of 450×10 ⁸ N/m ² .

【table】

[Table] Example 9 Rigidex 50 and 140-60 grade samples were sandwiched between metal plates at a temperature of 160℃, and after compression molding,
Cool to room temperature at a non-linear cooling rate of no more than 0.8°C per minute. A dumbbell-shaped sample with a length of 2 cm and a width of 0.5 cm is stretched using an Instron testing machine at 75°C. The test conditions and results are shown in Table-5. The significant difference in stretching behavior for samples with the same initial crystallinity is related to the broadening of the molecular weight distribution and therefore also to the molecular weight of the molecules in the amorphous phase. The optical micrograph of the isotropic sample of Rigidex 50 prepared by the method of this example shows regular orientation regions, but the isotropic sample of 140-60 shows a clear spherulite structure before stretching. It will be done.

[Table] Example 10 Rigidex 50, 140-60 grade BXP10 (
Samples of Rigidex 9 (n: 168000, w: 93800) were sandwiched between metal plates, compression molded at 160°C, and then cooled with water to room temperature. Length 2cm, width 0.5
A high stretching ratio can be obtained by stretching a cm dumbbell-shaped sample at 75°C for different times using an Instron tensile tester. The test conditions and results are shown in Table 6.

[Table] Example A High-density polyethylene (Uniphos DMDS2912 manufactured by Unihos Chemiat AB: Mw = 224000
and Mn=24000) at 235°C through a spinneret with a single orifice of 0.8 mm diameter.
The filament was extruded to obtain a filament, which was passed through a glycerin bath maintained at 110°C and wound up at a speed of 5 m/min. The distance between the spinneret and bath surface is approximately 10cm
The immersion time in the bath was 7.5 seconds. The isotropic filament produced in this way was then drawn in a conventional two-roll drawing frame through a glycerin bath at 120°C, the speed ratio of the feed roll and the drawing roll was 30:1, and the speed of the drawing roll was per minute. It was 48m. The drawing ratio of the drawn single fiber calculated from the initial and final cross sections was also 30. Room temperature Young's modulus is determined by the method of Gupta and Ward (J.
Macromol Sci. Phys. BI, 373 (1967)). Measured with a tester. The properties of this sample are shown in the attached table. Example B A portion of the spun filament of Sample A was drawn under the same conditions except that the drawing roll speed was 56 m/min and the draw ratio was 35. The physical properties of this sample were measured in the same manner as Sample A, and the results are shown in the table. Example C A portion of the spun monofilament of Sample A was drawn on the same drawing frame as Stretch A to a draw ratio of 30. However, the temperature was 120°C, the passing distance of the glycerin bath was shortened, and the stretching roll speed was 25 m/min. The physical properties of this sample were measured in the same manner as stretched sample A, and the results are shown in the table. Example High-density polyethylene (BP240 manufactured by BP Chemical Co., Ltd.: Mw = 26500, Mn = 26000 and melt flow index (BS105C method) 0.15)
was treated according to the method of the invention. Gauge dimension: 2cm x 0.5cm
dumbbell-shaped specimens were cut from 0.8 mm thick sheets compression molded at 160 °C between copper plates and then quenched in room temperature water. Stretching was carried out on an Instron Tencil test machine at a constant crosshead speed of 10 cm per minute and a temperature of 75°C. The resulting stretch ratio was determined by measuring the distance of ink marks made 0.1 cm apart on the original sample surface. The initial modulus is determined by the method of Gupta and Ward (J.
macromol.Sci.BI, 373 (1967)). The results are shown in the table. Example Compression molded sheet 110°C before cooling with room temperature water
The method of the example was repeated, except cooling to .
The initial modulus and stretch ratio of this sample are shown in the table. Example High-density polyethylene (Araton 7050 manufactured by EI Dupont: Mw = 60000 and Mn = 22000)
was extruded as a multifilament yarn at 275°C and wound at 120 m/min. The isotropic yarn produced in this manner was then drawn in a three-step drawing process on a heated plate at a final draw roll speed of 157 m/min and a total draw ratio of 45. The room temperature initial modulus at a strain level of 0.1% was determined by the method of Gupta and Ward (J.
Tenacity and elongation at break were measured on an Instron Tencil tester using Macromol.sci.Phys.BI373 (1967)) at an elongation rate of 50% per minute. The physical properties of this sample are shown in the table. Example High-density polyethylene (Araton 7050 manufactured by E.I. Dapon: Mw = 60000 and Mn = 22000)
was extruded as a multifilament yarn at 220°C and wound at 52 m/min. The isotropic yarn produced in this manner was drawn on a conventional two-roll drawing frame through a glycerin bath at 110°C. The speed ratio between the supply roll and the stretch roll was 25, and the stretch roll speed was 80 m/min. The room temperature initial modulus at a strain level of 0.1% was determined by the method of Gupta and Ward (J.Macromol.Sci.Phys.
BI373 (1967)), and the strength was measured using an Instron tensile tester at an elongation rate of 50% per minute. The physical properties of this sample are shown in the table.

【table】

【table】

【table】

【table】 [Brief explanation of the drawing]

Figures 1a to 1d show the method (1) of the present invention, respectively.
(4) This is a micrograph of the crystal structure of polyethylene produced by method (4).

Claims (1)

[Claims] 1 (1) High-density polyethylene with a weight average molecular weight of 200,000〓w＜300000 (w: weight average molecular weight), (2) High density with a weight average molecular weight (w)＜200000 and a number average molecular weight (n)〓20000 polyethylene, and (3) when weight average molecular weight (w) < 200000, number average molecular weight (n) < 20000 and n = 10 ⁴ ,
Selected from the group consisting of high-density polyethylene with Mw/n > 8 and w/n > 20 when n < 10 ⁴ , the Young's modulus when measured at room temperature under a strain of 0.1% for 10 seconds is 3×
10 High modulus oriented high density polyethylene stretched molded body having a value greater than ¹⁰ N/m ² .